Re: [Qemu-devel] [PATCH 22/31] ram: move migration_bitmap_mutex into RAMState

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Juan Quintela (quintela@redhat.com) wrote:
> Signed-off-by: Juan Quintela <quintela@redhat.com>
> ---
>  migration/ram.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 7f56b5f..c14293c 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -178,6 +178,8 @@ struct RAMState {
>      uint64_t xbzrle_overflows;
>      /* number of dirty bits in the bitmap */
>      uint64_t migration_dirty_pages;
> +    /* protects modification of the bitmap */
> +    QemuMutex bitmap_mutex;
>  };
>  typedef struct RAMState RAMState;
>  
> @@ -223,8 +225,6 @@ static ram_addr_t ram_save_remaining(void)
>      return ram_state.migration_dirty_pages;
>  }
>  
> -static QemuMutex migration_bitmap_mutex;
> -
>  /* used by the search for pages to send */
>  struct PageSearchStatus {
>      /* Current block being searched */
> @@ -626,13 +626,13 @@ static void migration_bitmap_sync(RAMState *rs)
>      trace_migration_bitmap_sync_start();
>      memory_global_dirty_log_sync();
>  
> -    qemu_mutex_lock(&migration_bitmap_mutex);
> +    qemu_mutex_lock(&rs->bitmap_mutex);
>      rcu_read_lock();
>      QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
>          migration_bitmap_sync_range(rs, block->offset, block->used_length);
>      }
>      rcu_read_unlock();
> -    qemu_mutex_unlock(&migration_bitmap_mutex);
> +    qemu_mutex_unlock(&rs->bitmap_mutex);
>  
>      trace_migration_bitmap_sync_end(rs->migration_dirty_pages
>                                      - num_dirty_pages_init);
> @@ -1498,7 +1498,7 @@ void migration_bitmap_extend(ram_addr_t old, ram_addr_t new)
>           * it is safe to migration if migration_bitmap is cleared bit
>           * at the same time.
>           */
> -        qemu_mutex_lock(&migration_bitmap_mutex);
> +        qemu_mutex_lock(&ram_state.bitmap_mutex);
>          bitmap_copy(bitmap->bmap, old_bitmap->bmap, old);
>          bitmap_set(bitmap->bmap, old, new - old);
>  
> @@ -1509,7 +1509,7 @@ void migration_bitmap_extend(ram_addr_t old, ram_addr_t new)
>          bitmap->unsentmap = NULL;
>  
>          atomic_rcu_set(&migration_bitmap_rcu, bitmap);
> -        qemu_mutex_unlock(&migration_bitmap_mutex);
> +        qemu_mutex_unlock(&ram_state.bitmap_mutex);
>          ram_state.migration_dirty_pages += new - old;
>          call_rcu(old_bitmap, migration_bitmap_free, rcu);
>      }
> @@ -1911,7 +1911,7 @@ static int ram_state_init(RAMState *rs)
>      int64_t ram_bitmap_pages; /* Size of bitmap in pages, including gaps */
>  
>      memset(rs, 0, sizeof(*rs));
> -    qemu_mutex_init(&migration_bitmap_mutex);
> +    qemu_mutex_init(&rs->bitmap_mutex);

Hmm - this isn't new, but....
ram_save_init is called from ram_save_setup; I don't see any
qemu_mutex_destroy's anywhere on bitmap_mutex.
So if you migrate, fail and then try again will you end up
calling qemu_mutex_init twice on that bitmap_mutex without
having destroyed it? And you'll have memset over it without
having destroyed it (that's new).

Dave

>      if (migrate_use_xbzrle()) {
>          XBZRLE_cache_lock();
> -- 
> 2.9.3
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK